The long-term goals of the proposed program are to further the understanding of the mechanisms of cellular immunity with an emphasis on lymphocyte mediators. These substances are elaborated by antigen or mitogen activated lymphocytes and are thought to play an important part in mediating cellular immunity or hypersensitivity. Our emphasis has been and will continue to be on one of these, migration inhibitory factor (MIF), which is measured by its ability to inhibit the migration of normal peritoneal macrophages out of capillary tubes and which appears to enhance the defense capacity of these cells. The specific goals of the proposed work are: Further characterization and investigation of the role of gucogangliosides on the macrophage as part of the receptor site for MIF and its relation to other macrophage membrane components; Characterization of a macrophage associated pH 5-MIF degrading proteinase and other proteinases associated with the macrophage; and Purification of MIF employing such refined purification methods as sucrose density gradient electrophoresis, sucrose density gradient isoelectrofocussing and affinity chromatography and investigation of the role of the two recently detected MIF species, pH 3-MIF and pH 5-MIF. Characterization on the basis of susceptibility to a macrophage proteinase and to trypsin has already been initiated.